Significance: Corneal cross-linking (CXL) is a well-known procedure for treating certain eye disorders such as keratoconus. However, characterization of the biomechanical changes in the cornea as a result of this procedure is still under active research. Specifically, there is a clinical need for high-resolution characterization of individual corneal layers.
Aim: A high-resolution elastography method in conjunction with a custom optical coherence tomography system is used to track these biomechanical changes in individual corneal layers. Pre- and post-treatment analysis for both low-dose and high-dose CXL experiments are performed.
Approach: A recently developed elastography technique that utilizes the theory of reverberant shear wave fields, with optical coherence tomography as the modality, is applied to pig corneas ex vivo to evaluate elasticity changes associated with corneal CXL. Sets of low-dose and high-dose CXL treatments are evaluated before and after treatments with three pairs of pig corneas per experiment.
Results: The reverberant three-dimensional (3D) optical coherence elastography (OCE) technique can identify increases in elasticity associated with both low-dose and high-dose CXL treatments. There is a notable graphical difference between low-dose and high-dose treatments. In addition, the technique is able to identify which layers of the cornea are potentially affected by the CXL procedure and provides insight into the nonlinearity of the elasticity changes.
Conclusions: The reverberant 3D OCE technique can identify depth-resolved changes in elasticity of the cornea associated with CXL procedures. This method could be translated to assess and monitor CXL efficacy in various clinical settings.
Optical coherence tomography-based elastography (OCE) can perform localized, quantitative measurements of biomechanical properties. One of the most promising applications of OCE is to measure corneal stiffness, which has been linked to keratoconus, corneal crosslinking, and laser vision correction, and can help improve diagnosis, screening and treatment monitoring. Various techniques have been demonstrated to determine the speed of elastic waves traveling in the cornea and thereby to measure the shear modulus of corneal tissues. Here we present a new approach based on a contact probe with a piezo-electrically vibrating tip. This wave generation approach is robust, provides extensive control over the temporal and spectral profiles of the mechanical stimulus, and allows us to measure traveling wave velocities a frequency range of 1 to 15 kHz. The shorter wavelengths obtained at high frequencies can improve the resolution of traveling wave elastography and enable measurements of stiffer tissues such as the sclera. Direct contact with the corneal surface are routinely performed for intraocular pressure measurements, which suggest that this approach has a path to clinical translation. Interestingly, we found that mechanical stimulation tends to excite a combination of guided and non-guided elastic waves, which must be considered for accurate calculation of the shear modulus and may affect other OCT elastography techniques.
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